Condensed tannins, also known as proanthocyanidins, are oligomeric or polymeric flavonoids composed of flavan-3-ol units. These units, such as catechin and epicatechin, polymerize to form complex structures. Flavonoid pigments, including anthocyanins and flavanols, share a common biosynthetic pathway with these tannins, and condensed tannins are directly related to the polymeric forms of flavan-3-ols.